MP3 patent free
With the expiration of US Patent 5,812,672 on 22 September 2015, both encoding and decoding of MP3 (MPEG-1 Audio Layer III) are probably patent-free in the United States. In most other countries it already was patent free.
It has been over 22 years since the publication of the MP3 spec in the MPEG-1 specification (as ISO/IEC 11172-3) on 12 August 1993. The near complete draft was published in September 1990. In many countries (such as European Union Countries), patents last 20 years and cannot be filed after publication, so in those countries, MP3 is patent-free. In the United States under pre-1995 law, patent continuations allowed patents to be extended, and so in the US, people had to wait for the expiration of US 5,812,67 for MP3 encoding and decoding to be patent free.
There are two unexpired US patents that are usually listed as MP3 patents (such as in What's the current status of mp3-licensing issues? email, A big list of mp3 patents, and on Technicolor's list). The first patent is US Patent 6,185,539. '539 was filed on 19 February 1997, so it is well after over three years after the MP3 spec was published, and so the spec counts as prior use. Secondly, looking at the claims, '539 is discussing MPEG-2, not MPEG-1, so it should probably not be counted as a MP3 patent. The other patent is US Patent 6,009,399 was filed on 16 April 1997 so it was filed even longer after the spec was published. Looking at its claims, it appears to be discussing an encoding optimization compared to standard MP3. So in my non-lawyer opinion, neither of these patents are likely to read on standard MP3 encoding and decoding.
I contacted Technicolor which licenses MP3 patents and asked if patent licensing was still needed for encoding and decoding MP3s. They replied but did not answer that question and stated that they do not license end users or individuals. I told them I was publishing my conclusions, so Technicolor could have chosen to provide me evidence I was wrong, and I would be writing a very different article.
Likelihood of valid unknown patents
If you are wondering how likely it is that there are other patents on MP3, it is unlikely. Because of the age of the MP3 specification, it is increasingly unlikely that any patents still exist for for it. Before 1995 in the United States, patents could be continued, but for those it would probably would take about 3 years for the patent to be granted, and then it would have a 17 year term from the grant date, which means it would expire by 2015. Current patent law in the United States and the European Union is 20 years after the filing date, so again, ones filed before the MP3 specification was published are expired.
Result of MP3 being patent free
As a practical matter, this is very good news for open source. MP3 is over 20 years old, but is still widely used. Finally, there is a common compressed audio format that Apple, Microsoft and Linux all can use patent free. Before the patents expired in the United States, either you illegally used open source, used a licensed binary, or went without using MP3s. On my main computer, the two types of binaries I had are firmwares, and the fluendo mp3 decoder. I can now get rid of the binary mp3 decoder. Fedora can finally support MP3s.
This article is a update on US Patent Expiration for MP3, MPEG-2, H.264
Disclaimers The author Josh Cogliati is not a lawyer, so if you are basing your multimillion dollar business on this, you are a fool. I am also a human, so there are almost probably errors in this. As well, these are my own opinions, not my employer's. This may be distributed verbatim, or may be modified and or distributed under a Creative Commons Attribution 3.0 Unported License.